This invention relates to trash compacting machines and the like, and particularly to the controls for a reversible electric motor, preferably an induction motor, driving a compacting ram in such a machine. Controls for the motor include a starting circuit with a manually operable starting switch which is closed to establish the power supply to the motor, as disclosed in U.S. Pat. Nos. 3,805,084 and 3,808,453. A directional switch is responsive to ram location at its retracted limit, also the cycle starting position, and is moved to cause forward (compacting) motor generation when the ram is at this position. When the ram leaves its starting position the directional switch transfers to reverse or retracting connections preparatory to any slowing of the motor to a speed where its centrifugal starting switch will again close.
A cycle ending switch is arranged to respond to ram movement as the ram approaches its starting position, at which time this switch is actuated and power to the motor is terminated as the ram approaches the starting position at the end of the retracting stroke. The ram and motor may coast to a stop, but once the starting position is reached, the directional switch is moved to the forward starting position.
A safety door interlock switch and a key switch are provided to assure that the machine can be operated only with the mechanism properly enclosed and protected, and only by authorized persons. The motor circuit includes overload protection and a manually operable stop switch. If any of these switches breaks the power supply to the motor after a compacting stroke has begun, immediately upon restoration of the power the motor normally will start in the reverse direction and retract the ram to its starting position.
It has been observed that trash subjected repetitively, but not in any particular sequence, to this type of compaction, will exhibit some tendency to rebound or expand after release of compacting pressure. Tests made by stopping the ram at its position of maximum force, where the motor stalls, have been made using the manual stop switch to turn off power to the motor at that time. The results of these tests indicate that by extending the period of time during which maximum force is exerted on the trash, the amount of rebound is substantially reduced, depending of course on the type of trash being compacted. However, beneficial results did not appear to be increased appreciably if this time period was extended beyond about thirty minutes. For example, application of continued force for as long as eight to twelve hours did not produce a really different result than the half-hour period.
Since it is necessary to have the ram retracted when loading the receptacle, an automatic or semi-automatic control for extending the period of high force compression is desirable. Especially is this so in connection with domestic models of trash compactors, where simplified operation is always desired.